1. Field of the Invention
The present invention relates to an apparatus for automatic dispensing of drugs. More particularly, the present invention relates to an apparatus for an animal which utilizes electromechanical mechanisms for dosing of drugs and a dispenser to ensure that the drug is delivered to the recipient.
2. State of the Art
It is well known in the fields of animal husbandry and veterinary medicine that it is usually desirable and often necessary to treat animals with drugs for parasites. The parasites of concern will often vary depending on the animal concerned and may include both ectoparasites and endoparasites. To eliminate or control these parasites, animals are often sprayed with or fed parasiticides, injected with parasiticide drugs, or provided with collars or other attachable devices that are saturated with a parasiticide. With farm animals, in order to control parasites, the farm animals typically must be rounded up and placed in a holding area so that each animal may be properly dosed with the drug(s). Once treated, the animal is released until the next dosing is required.
Unfortunately, rounding up the animals each month, etc., is time consuming and expensive. The animal must be located and then brought to a suitable location for administration of the drug. Because of the time and expense involved with such round-ups, the farmer is forced into a compromise of overdosing the animal with a very large dose of the drug to prolong the period during which the drug is present at levels which meet or exceed the minimum effective level, thereby decrease the frequency with which the drugs must be administered, or accepting the expense of frequent round-ups to repetitively doses the animals. For example, a topically applied drug may have an efficacy threshold which relates to a 750 milligram dose of a given medication. However, to extend the period between dosing, a significantly larger dose is typically used. In FIG. 1, there is shown a curve indicating a normal, exponentially declining (i.e., first-order) efficacy curve where the drug is provided by prior art diffusion devices, such as ear tags, at a very high initial dose in order to maintain drug levels above the efficacy threshold for a prolonged period.
Referring to FIG. 1, the initially high drug level 10 that is available early in the treatment period is typically much higher than the efficacy threshold 20. In the present example, the initially high drug level 10, is 3,750 milligrams, a drug level that would require a dose which is at least four to five times higher than the efficacy threshold for the drug used. Such large doses create several problems and negatively impact the animal by causing host toxicity, decreased weight gains, and loss of income to the animal handlers/owners.
An additional problem with the initial high dose is that high levels of the drug may still be present should the farmer desire to slaughter the animal within the time period correlated with the upper portion, indicated at 30, of the first-order declining kinetic curve. The high, persistent drug levels can limit the farmer's marketing response and potentially lead to adverse reactions in consumers.
In the FIG. 1 example, the drug, assumed to be a parasiticide for discussion purposes, which has been diffused onto/into the animal remains above the efficacy threshold for approximately 90 days. Once the amount of drug present falls below the efficacy threshold, the drug is present in insufficient amounts to adequately kill the targeted parasites. However, it is well known that the prolonged presence of subtherapeutic levels of a drug gives rise to the development of resistance to the drug within the targeted parasites. In a resistant parasite population, the efficacy threshold is shifted upward substantially. Therefore, due to use of prior art diffusion controlled dosage forms, numerous previously beneficial antibiotics and parasiticides are now of limited effectiveness because the target microbes and parasites have developed sufficient resistance to the drug to withstand even very high dosages that the host animal cannot tolerate. Drugs that are not biocides also are negatively impacted by this type of dosing pattern as manifested by enzyme down regulation and the clinical development of tachyphylaxis.
There have been numerous attempts to overcome these concerns. For example, it has been proposed to implant in farm animals devices which provide for the release of drugs at a time other than implantation. Examples of such devices are included in the U.S. Pat. Nos. 4,564,363, 4,326,522, 4,425,117, 4,439,197, 3,840,009, 4,312,347 and 4,457,752. Unfortunately, these devices tend to be expensive to use, typically they allow only for a one time (continuous) discharge of a single drug, and are otherwise disadvantageous.
Conventional collars for dogs, cats, and other domestic animals have met with limited success. While they are relatively inexpensive to purchase, they suffer from the same drawbacks as the aforementioned methods of administering parasiticides to farm animals. That is, the collar typically contains a relatively high concentration of the parasiticide when first used. The concentration, however, declines in a first-order declining kinetic curve (similar to that shown in FIG. 1) and thus may have the same drug resistant effect on the targeted parasite. Thus, there is a need for a method of administering drugs to animals which overcomes the disadvantages of the prior art.